The invention relates to a disc brake, in particular for a commercial vehicle.
In the functional case, that is to say in the case of a braking operation, the brake pads are applied by way of a brake application device first of all by the application-side brake pad being pressed against the brake disc and by the opposite, reaction-side brake pad subsequently being pressed. The brake caliper, which is configured as a sliding caliper, is displaced for this purpose counter to the application direction of the application-side brake pad.
After the brake is released, the brake caliper remains in this last-mentioned position in the case of the known sliding caliper disc brake, in which position the brake pads or at least the reaction-side brake pad bears against the brake disc in a pressureless but grinding manner. What are known as the “residual grinding moments”, which occur as a result during driving operation, lead to an increased fuel consumption of the vehicle and to a reduction in the service life both of the brake disc and the brake pads.
A slight release of the brake pads takes place during driving operation as a result of the movement of the brake disc and as a result of jolts and transverse accelerations when driving around bends. However, these effects are not sufficient to prevent the grinding effectively.
In order to avoid these disadvantages, DE 199 46 677 A1 has disclosed a disc brake in which a restoring device has a supporting part, which is mounted in the brake caliper and is guided slidingly on a guide spar of a fastening element, which is connected fixedly to the brake carrier and acts together with the supporting part as a sliding bearing.
If the brake caliper is displaced for pressing the reaction-side brake pad, the supporting part is pressed against an elastic restoring element which is configured as a compression spring and is intended to return the brake caliper into an initial position after the brake is released.
For wear-induced compensation of the air play, which compensation takes place on the application side by way of an adjusting device, the supporting part is mounted in a friction sleeve, which bears against the supporting part with static friction. Here, the coefficient of friction between the supporting part and the friction sleeve is selected in such a way that the friction sleeve adheres to the supporting part during normal braking operation, while it slides correspondingly on the supporting part, in a manner which overcomes the friction, during adjustment of the brake caliper by the adjusting device, until the adjusting stroke is reached.
However, the restoring of the brake caliper is exclusively dependent on the spring travel of the restoring element which is configured as a compression spring, which, however, does not make exact restoring possible to an always identical air play dimension between the brake disc and the reaction-side brake pad, with the result that the known brake disc represents a rather unsatisfactory solution of the problem.
The invention is therefore based on the object of developing a disc brake such that constant restoring of the brake caliper in relation to the air play is ensured.
This and other objects are achieved by a disc brake, particularly for a commercial vehicle, having: a) a brake caliper which straddles a brake disc and is configured as a sliding caliper; b) two brake pads, which are arranged in the brake caliper, can be moved in opposite directions and make contact with the brake disc in the functional position; c) at least one fastening element, which has a guide spar for fastening the brake caliper to a stationary brake carrier; d) a brake application device, by way of which the associated action-side brake pad can be pressed against the brake disc via at least one adjusting spindle; e) an adjusting device, which is connected in a rotationally locked manner on the adjusting spindle and by way of which a wear-induced change in an air play between the brake pads and the brake disc can be substantially compensated for; and f) a restoring device, which is arranged on the action side and has a restoring element which can be deformed elastically during the braking-induced displacement of the brake caliper, by way of which restoring device the brake caliper can be brought automatically into an initial position counter to the displacement direction during the brake application, wherein the restoring device has a supporting part, which remains in its position with respect to the brake carrier during the braking-induced displacement of the brake caliper and is operatively connected to the resilient restoring element with deformation of the latter.
In comparison with the prior art, in which the bush which forms a supporting part and is mounted on the guide spar slides on the guide spar during the braking-induced displacement of the brake caliper and is pressed against a resilient restoring element, the supporting part remains held on the guide spar, unchanged in its position, during the braking-induced displacement.
To this end, the supporting part is configured such that it bears with static friction against the guide spar, which is dimensioned such that the displacement force which is active during braking is not sufficient to overcome the static friction.
A greater force which displaces the supporting part on the guide spar by the adjusting stroke is active only when the adjusting device is actuated, by way of which adjusting device a wear stroke of the brake pads is compensated for.
As a result of the position of the supporting part which otherwise remains with respect to the guide spar, the resilient restoring element is deformed by the amount of the air play and, in the case of relief, that is to say when the braking operation is ended, is reset into its original position by exactly this amount, which corresponds to the air play, with driving of the brake caliper, that is to say with it being displaced counter to the application direction.
The supporting part and the restoring element can be, for example, configured in one piece, the supporting part being configured from a concentric bush, which surrounds the guide spar, and a plurality of lips which are arranged parallel to and at a spacing from one another, enclose the bush as rings, consist of an elastic, that is to say resilient material, and are incidentally deformed in their axial direction during the braking-induced displacement of the brake caliper with respect to the bush. When the braking operation ends, the lips which are incidentally connected fixedly to the brake caliper restore the brake caliper into its initial position on account of the inherent restoring forces, in accordance with the predefined air play.
According to a further aspect of the invention, the supporting part includes a static ring which bears against the guide spar with static friction and preferably fits into a circumferential inner groove of a receiving sleeve, on an end side of which the resilient restoring element is supported, which can be configured as a helical spring mounted directly or indirectly on the guide spar such that it can be displaced axially.
Instead of a static ring of this type in combination with the receiving sleeve which together form the supporting part, the supporting part can also include at least one clamping ring, preferably a packing of clamping rings which bear against the guide spar under prestress and therefore with the generation of static friction. Here, the restoring element in the form of the helical spring is also supported on the end side on a clamping ring, while the other end side of the helical spring bears against a shoulder of the brake caliper.
Clamping rings of this type are known as commercially available components and have, in each case, a continuous longitudinal slot for generating the prestress.
In the case of a braking-induced displacement of the brake caliper, the helical spring is compressed correspondingly, which helical spring bears at the other end directly against the brake caliper or against a part which is connected rigidly to the brake caliper. The spring force to be overcome is lower here than the holding force which is generated by the static friction of the supporting part. The result is that the brake caliper slides on the receiving sleeve which receives the static ring or on the clamping rings. The static friction of the supporting part is overcome and this is forwarded correspondingly, until the extent of the wear stroke is reached, only in the case of a greater force which acts on the helical spring and an associated increase in the spring force, as results during the wear-induced adjustment of the brake caliper.
Two fastening elements are usually provided in a disc brake, by way of which fastening elements the brake caliper is held on the brake carrier such that it can be displaced axially in the direction of the brake disc. Here, one connecting region is configured as a locating bearing and the other connecting region is configured as a floating bearing, in each case as sliding bearings, however.
Since the locating bearing requires, as a result of its function, a relatively large amount of installation space, above all a relatively large overall length, this region is suitable for placing the restoring device. In a supplementary manner, in the case of unfavorable installation conditions and a high restoring force requirement, a restoring device can additionally be used in the floating bearing.
In this case, the required restoring force and the clamping force of the supporting parts, that is to say their static friction on the guide spar, are divided over both restoring devices. The restoring force is expediently higher at the locating bearing than at the floating bearing. It can be sufficient here to equip the restoring device of the floating bearing with an elastomer ring which is provided with the circumferential elastic lips, while the locating bearing is to be provided with one or more clamping rings.
The embodiment in which the supporting part includes a packing of clamping rings can be realized in two different possible designs. In a first variant, the maximum possible moving force of the restoring element, that is to say of the restoring spring, is lower than the minimum possible adjusting force of the adjusting device. Here, in the case of adjusting operations, the brake caliper is pulled onto the brake disc with the reaction-side brake pad, counter to the force of the restoring spring. The entire air play is then on the action side and is set there as overall air play. To this extent, this is identical to disc brakes without an active caliper restoring device.
After the air play is set or after a braking operation has taken place, the restoring device resets the brake caliper by the predefined amount and thus generates the air play on the reaction side. The overall air play is thus set exclusively by the adjusting device. The division of the overall air play to the action (inner) side and reaction side (outer side) is determined by the caliper restoring means.